Which command enables you to view the exact timestamp when a link goes down in the network?

To determine when a link goes down in a network, the correct command is the one that displays system log messages, which includes detailed events and actions taken by the device. Specifically, the command that retrieves these system log messages shows timestamps for various events, such as link state changes. This includes when a link goes down, along with the exact time it occurred.

The system log captures a wide range of operational details, making it the most appropriate choice for pinpointing specific events like link failures. By using this command, an administrator can accurately track network events and monitor the overall health of the network.

Other commands listed might provide useful information as well, but they do not emphasize the tracking of specific events like link status changes in the same detailed manner as the messages command. For example, some commands may focus on alarms or current interface statuses without providing the historical context or timestamps needed for full diagnostics of link failures.